The present invention relates to an apparatus having a controllable dwell and, more particularly, to a drilling apparatus having an adjustable dwell mechanism and associated method.
The production of components of an assembly, for example, airplane structural components, often requires that holes be drilled in the components to accommodate the fasteners that secure the assembly together. In some instances, the drilled holes may also need to be countersunk. Typically, the countersink has a preferred depth where the diameter of the countersink is matched to the fastener being used. If the countersink is not deep enough, the fastener may protrude outwardly of the component surface. If the countersink is too deep, particularly in a thin-section component, the hole associated with the countersink may be unacceptably large, the structural strength of the component may be adversely affected, and the fastener may not be able to securely fasten the component. In addition, the excess countersink depth, after the fastener has been installed, will define a cavity which may undesirably collect debris or disrupt airflow about the component. Further, since these components are generally fabricated in a manufacturing operation, where multiple holes must be drilled and countersunk in one or more components, consistency of the countersink depth is also typically required.
In some manufacturing operations, drilling and/or countersinking processes may be performed with, for example, portable pneumatic power feed equipment. In these situations, a pneumatic drill motor is used to turn a cutter while a feed mechanism feeds and retracts the cutter over a predetermined distance. The relative positioning of the component or workpiece with respect to the travel of the cutter determines the depth of the hole and or countersink. In practice, the power feed equipment must also incorporate a dwell into the feed/retract cycle of the cutter when the cutter is at the feed limit and before it is retracted. The dwell, or pause in the feed cycle at the feed limit, facilitates consistency in the countersink diameter by allowing a period for the cutter to clean up the countersink surface by removing any extraneous material from the countersink. The dwell also allows a flexible workpiece or other flexible components of the power feed equipment to spring back to their original shape if deformed by the feed force exerted by the feed mechanism feeding the cutter. Thus, obtaining a consistent countersink diameter within specified tolerances using pneumatic power feed equipment generally requires a controllable dwell that is both adjustable and consistently repeatable.
Some typical pneumatic countersinking or drilling/countersinking equipment combine dwell and automatic retract features into the same mechanism. For example, in one instance, a microstop-type adjustable stop is used to control the closing of an air vent port at a point in the cutter feed cycle. The air vent port is generally configured to vent air from a pressurized air source that is also connected to the retract mechanism. As the cutter reaches the feed limit during the feed cycle, the vent port is sealed which causes back-pressure to accumulate. Once the back-pressure reaches a threshold pressure, a spool valve in the retract mechanism is shifted and thereby actuates the retract portion of the feed cycle. In some instances, an adjustable needle valve is included in the dwell and automatic retract mechanism for controlling the amount of air flowing out through the vent port and thereby providing the dwell portion of the mechanism. Generally, an increased restriction of the air flow out through the vent port by the needle valve will result in an increased time between the vent port being sealed and the back-pressure reaching the threshold pressure, thereby providing a dwell between the cutter reaching the feed limit and the spool valve shifting to actuate the retract portion of the feed cycle.
However, this dwell and automatic retraction mechanism may produce unacceptable variances in the amount of dwell between cutter feed cycles. For example, one of the factors affecting the dwell is the relative friction between the spool valve and the bore housing the spool valve. Generally, as the friction between the spool valve and its bore increases, the dwell will also increase for a given dwell adjustment of the needle valve. This friction may further depend on, for instance, the lubrication between the spool valve and the bore or the amount of moisture or particulates in the air supply. These factors, along with the air supply pressure, may vary greatly and frequently in a typical manufacturing environment. Fluctuations in the air pressure will also cause the dwell to vary for a given dwell adjustment of the needle valve.
Another factor possibly adversely affecting the consistency of the dwell is the configuration of the dwell portion of the mechanism. The needle valve controlling the amount of air flowing through the vent port typically comprises a relatively small passage for transporting the air from the air supply. Thus, the needle valve may be sensitive to particulates in the air supply which will tend to accumulate in the needle valve, thereby impeding the air flow and causing the adjustment of the dwell to vary.
Still further, in some instances, if the dwell and automatic retraction mechanism is set for a relatively short dwell, the cutter may be retracted by the retraction mechanism before the feed portion of the feed cycle is fully completed. That is, the feed force generated by the feed mechanism, which is the force that generally feeds the cutter, may not have sufficient dwell time to be transferred to the depth stop at the feed limit before the cutter is retracted. Thus, the cutter may be retracted prematurely, thereby possibly resulting in a shallow countersink in the workpiece.
Thus, there exists a need for pneumatic power feed equipment, particularly equipment used in drilling and or countersinking processes in a manufacturing operation, having a controllable dwell that is both adjustable and consistent between drilling and or countersinking processes. Such a dwell mechanism should desirably be substantially independent of the retraction mechanism and relatively insensitive to fluctuations in the pressure of the air supply as well as to the condition and or purity of the air provided by the air supply. The dwell mechanism should also be configured such that the feed force is transferred to the depth stop before the retraction mechanism can be actuated to reduce the possibility of shallow countersinks.
The above and other needs are met by the present invention which, in one embodiment, provides an apparatus having a controllable dwell for drilling and or countersinking a hole in a workpiece. The apparatus generally comprises a feed mechanism, a retraction mechanism, and a dwell mechanism. The feed mechanism is configured to feed a spindle from a starting position to a predetermined feed limit during a feed cycle. The retraction mechanism is configured to retract the spindle from the feed limit to the starting position to complete the feed cycle. The dwell mechanism is in communication with the retraction mechanism and comprises a mechanical bias member that stores energy during at least a portion of the feed cycle, wherein the mechanical bias member releases at least a portion of the energy once the spindle reaches the feed limit. The retraction mechanism is only actuated once the spindle reaches the feed limit and the mechanical bias member releases at least a portion of the energy. A predetermined dwell period is thereby provided between the spindle reaching the feed limit and the retraction mechanism being actuated.
In some instances, the retraction mechanism is configured to be pneumatically controlled. The apparatus thus further comprises a pressurized air supply operably connected to the retraction mechanism and to a scalable vent port, wherein the vent port is sealed at least when the spindle is at the feed limit. Accordingly, the dwell mechanism may also be operably connected to the air supply intermediate the vent port and the retraction mechanism and may further comprise a mounting member, a hydraulically-actuated device, and an adjusting member.
The mounting member may define an exhaust port and a mounting port, wherein the exhaust port is in communication with the air supply. Accordingly, the hydraulically-actuated device comprises a housing with a reduced portion extending through and sideably disposed within the mounting port. The housing generally has a shoulder adjacent to the reduced portion, wherein the shoulder is capable of engaging and sealing the exhaust port in the mounting member. The device further includes a slidable piston member communicating with the feed mechanism and interacting with the housing such that the device is capable of adjustably dissipating a feed force applied thereto by the feed mechanism. To dissipate the feed force, the device slides with respect to the mounting port such that the shoulder is disengaged from the exhaust port as the feed force is dissipated. The adjusting member operably engages the reduced portion of the housing opposite the mounting member from the shoulder and the mechanical bias member is disposed intermediate the adjusting member and the mounting member. The mechanical bias member releases at least a portion of the stored energy by applying a restoration force which urges the shoulder to re-engage the exhaust port after the spindle has reached the feed limit and the feed force has been dissipated. The retraction mechanism is then actuated when the exhaust port is resealed.
Generally, the adjusting member cooperates with the mechanical bias member to adjust the restoration force. More particularly, the mechanical bias member may comprise a Belleville washer and the adjusting member may comprise an adjusting nut threadedly engaged with the reduced portion of the housing. The adjusting nut thereby cooperates with the Belleville washer such that increased compression of the Belleville washer by the adjusting nut increases the restoration force and thereby reduces the dwell period. In some instances, the apparatus may comprise a depth stop mechanism operably connected to the feed mechanism for controlling the feed limit. The apparatus may further comprise, for example, a pneumatic drill having a drill motor for rotating the spindle, wherein the spindle is further adapted to engage a cutter. The cutter is typically capable of drilling and or countersinking a hole in a workpiece.
In one particularly advantageous embodiment, an apparatus having a controllable dwell for drilling and or countersinking a hole in a workpiece comprises a spindle, a plate defining a bore, a feed mechanism operably engaging the plate, an air supply in communication with the feed mechanism, a retraction mechanism, and a dwell mechanism. The feed mechanism is configured to feed the spindle through the bore to an adjustable predetermined feed limit during a feed cycle. The air supply supplies pressurized air to a vent port through a supply line, wherein the vent port is sealed at least when the spindle is at the feed limit. The retraction mechanism is in communication with the supply line and is capable of retracting the spindle.
The dwell mechanism is in communication with the supply line intermediate the vent port and the retraction mechanism and generally comprises a mechanical bias member, a mounting member, a hydraulically-actuated device, and an adjusting member. The mechanical bias member stores energy during at least a portion of the feed cycle and releases at least a portion of the energy once the spindle reaches the feed limit. The retraction mechanism is only actuated once the spindle reaches the feed limit and the mechanical bias member releases at least a portion of the energy. A predetermined dwell period is thereby provided between the spindle reaching the feed limit and the retraction mechanism being actuated.
The mounting member defines an exhaust port and a mounting port, wherein the exhaust port is in communication with the air supply. The hydraulically-actuated device comprises a housing having a reduced portion extending through and slidably disposed within the mounting port. The housing further has a shoulder adjacent to the reduced portion which is capable of engaging and sealing the exhaust port. The device further includes a slidable piston member communicating with the feed mechanism and interacting with the housing such that the device is capable of adjustably dissipating a feed force applied thereto by the feed mechanism. The device dissipates the feed force by sliding with the respect to the mounting port such that the shoulder is disengaged from the exhaust port as the feed force is dissipated. The adjusting member operably engages the reduced portion of the housing opposite the mounting member from the shoulder. The mechanical bias member is disposed intermediate the adjusting member and the mounting member and releases at least a portion of the stored energy by applying a restoration force which urges the shoulder to re-engage the exhaust port after the spindle has reached the feed limit and the feed force has been dissipated. The retraction mechanism is then actuated when the exhaust port is resealed.
A further advantageous aspect of the present invention comprises a method of providing a dwell period in an apparatus. Generally, a spindle is fed axially from a starting position to a predetermined feed limit during a feed cycle. During at least a portion of the feed cycle, energy is stored in a mechanical bias member. The spindle is then maintained at the feed limit for a predetermined dwell period, where at least a portion of the stored energy is released from the mechanical bias member once the spindle reaches the feed limit. The spindle is then retracted from the feed limit to the starting position once the mechanical bias member releases at least a portion of the stored energy. In some instances, the method may further comprise actuating a feed mechanism before feeding the spindle. Also, in some instances, a feed force may be generated with the feed mechanism as the feed mechanism feeds the spindle toward the feed limit, wherein the feed force may be dissipated with a hydraulically-actuated device. As the device dissipates the feed force, it is disengaged from an exhaust port defined by a mounting member to thereby unseal the exhaust port. The feed mechanism is then stopped by a depth stop mechanism once the spindle has reached the feed limit, thereby discontinuing generation of the feed force. As the spindle is maintained at the feed limit, the device is urged back into a sealing engagement with the exhaust port, after the feed mechanism has been stopped by the depth stop mechanism, such that the device reseals the exhaust port after the feed force is dissipated and the mechanical bias member has released at least a portion of the stored energy. The spindle is then retracted after the device has resealed the exhaust port.
Thus, a drilling apparatus having a controllable dwell according to embodiments of the present invention is capable of providing a controllable dwell that is both adjustable and consistent between drilling and or countersinking processes in a manufacturing operation. Since the dwell mechanism is mechanically implemented with the mechanical bias device, such as a Belleville washer, a more repeatable and adjustable dwell mechanism is provided that is substantially unaffected by the characteristics of the retraction mechanism, moisture or particulates in the air supply, or the pressure of the air supply. Since no needle valve is necessary in the dwell mechanism according to embodiments of the present invention, there are no minute restrictions between the air supply and the vent port which would be susceptible to contaminants in the air supply. In addition, the retraction mechanism is not actuated until the feed force has been transferred to the depth stop mechanism, thereby preventing premature actuation of the retraction mechanism which causes shallow countersinks. The dwell mechanism according to embodiments of the present invention therefore provides a more consistent and controllable dwell as compared to the prior art.